This application claims the priority of German application 197 17 026.9, filed in Germany on Apr. 23, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an extrusion arrangement for manufacturing hollow-profile workpieces made of metal as well as to a process for manufacturing hollow-profile workpieces made of metal.
Preferred embodiments of the invention relate to extrusion arrangements of the type having an extrusion die which is guided in an extrusion chamber and compresses material situated in the extrusion chamber and, for forming an extruded hollow profile, presses the material through a bottom die arranged on the head-side end of the extrusion chamber, during the emerging from the bottom die into at least one forming tool adjoining an outlet opening of the bottom die, a forming of the extruded hollow profile taking place by means of internal high pressure.
Extruded hollow profiles produced by means of known extrusion arrangements and processes of this type are extruded as cut goods in the hot state and are stretched after their cooling. This stretching is necessary because, during the cooling, a hot-pressed profile is subjected to a warping and a shrinking of the material so that the outer dimensions of the extruded profile will change which has the result that the required measures are not met. For stretching the extruded profile, so-called collets are applied to sections provided for this purpose at the ends of the extruded profiles. After the stretching, these sections are removed for applying the collets and the profile is cut to the ordered measurements. After the cutting, the sections are available for being built in or for further processing. In the latter case the hollow extruded profile is brought into the desired shape, for example, by means of a known bending or forming process.
For this purpose, it is known from German Patent Document DE 44 25 984 A1 to place an extruded hollow profile in a mold corresponding to the component to be manufactured and then, by introducing a pressure medium in the hollow space of the extruded hollow profile, bulge or expand the extruded hollow profile until it is in contact with the mold surface, the supplied pressure medium being tempered so that the wall area of the extruded hollow profile to be deformed is brought in a controlled manner to a temperature above the ambient temperature in order to improve the deformability of the metallic material.
From German Patent Document DE 43 29 812 A1, it is known to insert a blank, which is made of an aluminum alloy and is cast in a billet shape, in a casting chamber in which the blank is inductively heated to a temperature which is higher than the hardening temperature but lower than the melting temperature of the aluminum alloy. This partially liquid, partially solid blank is then pressed by operating a casting plunger from the casting chamber into the hollow space of a mold, where the blank flows around a cooled arbor for forming a bore in the tube-shaped body to be manufactured.
From the processing of plastic materials, the so-called extrusion blow forming is known (compare Extrusion Blow Forming, VDI Publishers, Dusseldorf, 1979, Page 3, and on) in the case of which a hose-shaped preform is extruded and, by means of blowing air fed into the interior of the hose-shaped preform, is shaped to the finished part without any intermediate thermal treatment in the thermoplastic condition.
Based on the above, it is an object of the invention to provide an extrusion arrangement and a process for manufacturing hollow-profile workpieces by means of which, for manufacturing hollow-profile workpieces from metal, a continuous extrusion process is permitted with a piece manufacturing at the outlet of the billet without the requirement of an intermediate treatment of the extruded hollow profile, such as stretching, cooling, heating and the like.
For achieving this object, an extrusion arrangement is proposed according to the invention wherein a plurality of forming tools are provided for receiving an extruded hollow profile and forming same, said plurality of forming tools being alternately arranged adjoining the outlet opening of the bottom die and, for cooling and releasing the formed extruded hollow profile, being removable from the bottom die.
In the case of the extrusion arrangements according to the invention, the emerging from the bottom die is followed immediately by a forming of the extruded hollow profile by internal high pressure so that, while utilizing the process heat and without additional heating, a postforming of the extruded hollow profile is permitted. Especially in the case of aluminum materials, the forming can be carried out by means of hot forming at low differential pressures which, however, must be applied for a relatively long time period. According to the invention, a higher pressure admission takes place for a short time in that a suitable fluidic medium (gaseous or liquid) is fed into the interior of the extruded hollow profile particularly from the machine side during the extrusion.
As a further development of the invention, an arbor is provided with a bore which can be acted upon by a pressure medium and which is connected with the interior of the extruded hollow profile. As a result, a particularly simple feeding of the pressure medium into the interior of the extruded hollow profile is permitted.
In a further development of the invention, the bottom die is a hollow-chamber bottom die which has a connection which can be acted upon by a pressure medium and is connected with the interior of the extruded hollow profile, which also permits a particularly simple feeding of the pressure medium into the interior of the extruded hollow profile.
In a further development of the invention, a forming tool is provided which adjoins an outlet opening of the bottom die, whereby a precise forming of the extruded hollow profile is ensured. This forming tool advantageously has an at least two-part construction in order to facilitate a release of the formed extruded hollow profile.
In a particularly advantageous further development of the invention, a plurality of forming tools are provided which alternately can be arranged for receiving an extruded hollow profile and its forming adjoining the outlet opening of the bottom die and can be removed for the cooling and releasing of the formed extruded hollow profile from the bottom die. This further development of the extrusion arrangement according to the invention prevents that the release and the cutting-off of the formed extruded hollow profile impairs the extruding rate of the extrusion arrangement. In that several forming tools are alternately arranged to be adjoining the outlet opening of the bottom die, a continuous extruding process is possible with an integrated hot forming of the extruded hollow profile.
As a further development of the invention, the forming tools are arranged in the manner of a rotational change system in the extruding direction behind the bottom die, or they are arranged as a linear adjusting and displacing system in the extruding direction behind the bottom die.
Also for achieving the object on which the invention is based, a process is suggested for manufacturing hollow-profile workpieces made of metal having the characteristics according to which the interior of the extruded hollow profile for the forming from the process heat is acted upon by a pressure medium.
In especially advantageous preferred embodiments of the invention, the forming of the extruded hollow profile takes place in a forming tool.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.